Program Director/Principal Investigator (Last, First, Middle): Hennebold, Jon PHS 398/2590 (Rev. 11/07) Page Continuation Format Page ABSTRACT The long-term objective of this research is to define the mechanisms occurring within the primate corpus luteum (CL) that are critical for its development and regression. Evidence obtained from nonprimate species indicates that prostaglandins (PGs) regulate luteal structure-function, but their role in primate luteal physiology have not been defined. Recent preliminary data have demonstrated that the expression of PGE2 synthesis (prostaglandin-endoperoxide synthase 2 or PTGS2;microsomal PGE2 synthase-1 or PTGES) and signaling (PGE2 receptor 3 or PTGER3) components peak in the rhesus macaque CL through the period of its development. Moreover, expression of the PGE2 synthesizing and signaling components significantly decreased preceding the period of functional regression of the CL, which also coincided with increasing levels of PGF2_ receptor (PTGFR) expression. Thus, experiments will be performed to test the hypothesis that PGE2 actions are critical for primate luteal development, while PGF2_ serves as a critical intraluteal initiator and/or effector of luteolysis. Studies using rhesus macaques are proposed that will assess the role PGE2 signaling plays in the development of the primate CL (Aim 1) and evaluate whether PGF2_ signaling is required for the demise of the CL at the end of the luteal phase (Aim 2). Protocols blocking intraluteal PG synthesis via a PTGS2 selective inhibitor will determine their role in CL development. The ablation of PG synthesis in the developing CL will be combined with the restoration of PTGER3 signaling through the use of a selective PTGER3 agonist. The intraluteal delivery of a PTGFR antagonist prior to the onset of luteal regression will establish the role of PGF2_ in luteolysis. Daily concentrations of serum progesterone, first day of menses, and CL weight will be used to evaluate luteal function and lifespan. Histochemical markers of apoptotic, endothelial, and steroidogenic cells will be used for morphologic analysis of CL structure, while the expression of LH-regulated steroidogenic and angiogenic factors will be quantified to evaluate the relationship between PG signaling and luteal function. These studies will provide novel insight into the role of PG actions in luteal development and regression in primates. Such an understanding of PG involvement in the regulation of luteal structure-function may aid in our undestanding of infertility or other disorders associated with luteal dysfunction.